Reaction system for growing a thin film

ABSTRACT

An atomic deposition (ALD) thin film deposition apparatus includes a deposition chamber configured to deposit a thin film on a wafer mounted within a space defined therein. The deposition chamber comprises a gas inlet that is in communication with the space. A gas system is configured to deliver gas to the gas inlet of the deposition chamber. At least a portion of the gas system is positioned above the deposition chamber. The gas system includes a mixer configured to mix a plurality of gas streams. A transfer member is in fluid communication with the mixer and the gas inlet. The transfer member comprising a pair of horizontally divergent walls configured to spread the gas in a horizontal direction before entering the gas inlet.

RELATED APPLICATIONS

This application claims the priority benefit under 35 U.S.C. §120 toU.S. application Ser. No. 11/333,127, filed on Jan. 17, 2006, issuedJun. 26, 2012 as U.S. Pat. No. 8,211,230 and under 35 U.S.C. §119(e) ofProvisional Application No. 60/645,581, filed on Jan. 18, 2005 andProvisional Application No. 60/656,832, filed Feb. 24, 2005, the entirecontents of these applications are hereby incorporated herein byreference in their entirety

BACKGROUND OF THE INVENTION

The present invention relates to equipment for chemical processes. Inparticular, the present invention relates to equipment for growing athin film in a reaction chamber.

DESCRIPTION OF THE RELATED ART

There are several vapor deposition methods for depositing thin films onthe surface of substrates. These methods include vacuum evaporationdeposition, Molecular Beam Epitaxy (MBE), different variants of ChemicalVapor Deposition (CVD) (including low-pressure and organometallic CVDand plasma-enhanced CVD), and Atomic Layer Epitaxy (ALE), which is morerecently referred to as Atomic Layer Deposition (ALD).

ALD is a known process in the semiconductor industry for forming thinfilms of materials on substrates such as silicon wafers. ALD is a typeof vapor deposition wherein a film is built up through self-saturatingreactions performed in cycles. The thickness of the film is determinedby the number of cycles performed. In an ALD process, gaseous precursorsare supplied, alternatingly and repeatedly, to the substrate or wafer toform a thin film of material on the wafer. One reactant adsorbs in aself-limiting process on the wafer. A subsequent reactant pulse reactswith the adsorbed material to form a single molecular layer of thedesired material. Decomposition may occur through reaction with anappropriately selected reagent, such as in a ligand exchange or agettering reaction. In a typical ALD reaction, no more than a molecularmonolayer forms per cycle. Thicker films are produced through repeatedgrowth cycles until the target thickness is achieved.

In an ALD process, one or more substrates with at least one surface tobe coated and reactants for forming a desired product are introducedinto the reactor or deposition chamber. The one or more substrates aretypically placed on a wafer support or susceptor. The wafer support islocated inside a chamber defined within the reactor. The wafer is heatedto a desired temperature above the condensation temperatures of thereactant gases and below the thermal decomposition temperatures of thereactant gases.

A characteristic feature of ALD is that each reactant is delivered tothe substrate in a pulse until a saturated surface condition is reached.As noted above, one reactant typically adsorbs on the substrate surfaceand a second reactant subsequently reacts with the adsorbed species. Asthe growth rate is self-limiting, the rate of growth is proportional tothe repetition rate of the reaction sequences, rather than to thetemperature or flux of reactant as in CVD.

To obtain self-limiting growth, vapor phase reactants are kept separatedby purge or other removal steps between sequential reactant pulses.Since growth of the desired material does not occur during the purgestep, it can be advantageous to limit the duration of the purge step. Ashorter duration purge step can increase the available time foradsorption and reaction of the reactants within the reactor, but becausethe reactants are often mutually reactive, mixing of the vapor phasereactants should be avoided to reduce the risk of CVD reactionsdestroying the self-limiting nature of the deposition. Even mixing onshared lines immediately upstream or downstream of the reaction chambercan contaminate the process through parasitic CVD and subsequentparticulate generation.

SUMMARY OF THE INVENTION

To prevent the vapor phase reactants from mixing, ALD reactors mayinclude an “inert gas valving” or a “diffusion barrier” arrangement in aportion of a supply conduit to prevent flow of reactant from a reactantsource to the reaction chamber during the purge step. Inert gas valvinginvolves forming a gas phase, convective barrier of a gas flowing in theopposite direction to the normal reactant flow in the supply conduit.See T. Suntola, Handbook of Crystal Growth III, Thin Films and Epitaxy,Part B: Growth Mechanisms and Dynamics, ch. 14, Atomic Layer Epitaxy,edited by D. T. J. Hurle, Elsevier Science V.B. (1994), pp. 601-663, thedisclosure of which is incorporated herein by reference. See especially,pp. 624-626. Although such prior art arrangements have been successfulin preventing vapor phase reactants from mixing, there is still room forimprovement. In particular, experimental studies have indicated thatwithin the reactor chamber there are dead pockets and/or recirculationcells that are difficult to purge. Accordingly, a portion of previousreactant pulse may remain in the reaction chamber during the subsequentreactant pulse. This may disadvantageously lead to CVD growth within thereaction chamber and on the substrate itself. CVD growth within thereaction chamber may disadvantageously lead to increased particleemissions.

A need therefore exists for an improved reactor design which is easierto purge and eliminates or significantly reduces dead pockets in whichreactants may remain after a purging step.

Accordingly, one embodiment of the present invention comprises an atomicdeposition (ALD) thin film deposition apparatus that includes adeposition chamber configured to deposit a thin film on a wafer mountedwithin a space defined therein. The deposition chamber comprises a gasinlet that is in communication with the space. A gas system isconfigured to deliver gas to the gas inlet of the deposition chamber. Atleast a portion of the gas system is positioned above the depositionchamber. The gas system includes a mixer configured to mix a pluralityof gas streams. A transfer member is in fluid communication with themixer and the gas inlet. The transfer member comprising a pair ofhorizontally divergent walls configured to spread the gas in ahorizontal direction before entering the gas inlet.

Another embodiment of the present invention comprises an atomic layerdeposition (ALD) thin film deposition apparatus that comprises adeposition chamber configured to deposit a thin film on a wafer mountedwithin a space defined therein. The deposition chamber includes a gasinlet that is in communication with the space. The deposition chamberfurther comprising a sealing portion that includes a sealing surface. Asusceptor is configured to support the wafer within the space. Thesusceptor configured to move vertically with respect to the depositionchamber between a first position in which the susceptor seals againstthe sealing surface and a second, lower position in which the susceptorno longer seals against the sealing surface. In the first position, avertical distance between the interface between the sealing surface andthe susceptor and the wafer positioned on the susceptor is less thanabout 2 millimeters.

Another embodiment of the present invention comprises a substratesupport for processing semiconductor substrates. The substrate supportcomprises a top surface with a recess. The recess is configured suchthat the top surface of the substrate support only contacts thesubstrate along an edge portion of the substrate.

Another embodiment of the present invention comprises an deposition(ALD) thin film deposition apparatus that includes a deposition chamberconfigured to deposit a thin film on a wafer mounted within a spacedefined therein. The deposition chamber comprises a gas inlet that is incommunication with the space. The deposition chamber further comprises asealing portion that includes a sealing surface. A susceptor isconfigured to support the wafer within the space. The susceptor isconfigured to move vertically with respect to the deposition chamberbetween a first position in which the susceptor seals against thesealing surface and a second, lower position in which the susceptor nolonger seals against the sealing surface. The susceptor is configuredsuch that when the wafer is positioned on the susceptor in the firstposition, the leading edge of the wafer, with respect to gas flow, ispositioned further from the sealing surface as compared to the trailingedge of the wafer.

These and other objects, together with the advantages thereof over knownprocesses and apparatuses which shall become apparent from the followingspecification, are accomplished by the invention as hereinafterdescribed and claimed.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is front, top and left side a perspective view of an atomiclayer deposition (ALD) device.

FIG. 1B is a bottom, back and left side perspective view of the ALDdevice from FIG. 1A.

FIG. 2 is a cut-away perspective of the ALD device of FIG. 1, cut alonglines 2-2.

FIG. 3 is a perspective view of the gas distribution system within theALD device of FIG. 1A (partially visible in FIG. 2).

FIG. 4 is a top plan view of the reactant gas lines coupled to anupstream member of the mixer assembly of the gas distribution systemfrom FIG. 3 showing a buffer region in each reactant gas line.

FIG. 5 is a schematic cross-sectional view through a portion of thegas-distribution system and reactor chamber of the ALD device of FIG.1A.

FIG. 6 is a perspective view of a portion of a modified embodiment of agas distribution system that is coupled to a top plate of a reactionchamber within an ALD device.

FIG. 7 is a top plan view of the gas distribution system of FIG. 6.

FIG. 8 is a top plan view of the top plate of FIG. 6 with the gasdistribution system removed.

FIG. 9 is a cross-sectional view taken along line 9-9 of FIG. 7.

FIG. 9A is an enlarged view of a portion of FIG. 9.

FIG. 10 is a schematic illustration of a susceptor, a substrate and abottom plate of a reactor within the ALD system of FIG. 1.

FIG. 11 is a cross-sectional view similar to FIG. 9 but alsoillustrating a susceptor and bottom plate of the ALD device.

FIG. 12 is a partial top perspective view of the susceptor and bottomplate of FIG. 11.

FIG. 13 is a top perspective view of the susceptor of FIG. 11 rotated180 degrees.

FIG. 14 is a cross-sectional view taken through line 14-14 of FIG. 13and further illustrating a substrate positioned on the susceptor.

FIG. 15 is a schematic cross-sectional illustration of an edge portionof an embodiment of a lift pin and susceptor arrangement.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1A is a perspective view of an embodiment of an ALD device 100. TheALD device 100 comprises a top member 110, a bottom member 112, and afront member 118, which together form a portion of a housing for the ALDdevice 100. In the embodiment illustrated in FIG. 1A, an upper heater114 extends through the top member 110. The upper heater 114 isconfigured to maintain the temperature in the upper portion of the ALDdevice 100. Similarly, a lower heater 116 extends through the bottommember 112. The lower heater is configured to maintain the temperaturein the lower portion of the ALD device 100.

The front member 118, which serves as a gate valve, of the ALD device100 covers an opening 120. A dashed line outlines the opening 120 inFIG. 1A. Once the front member 118 is removed, the opening 120 canreceive a wafer to be processed by the ALD device 100. In this way, thereceived wafer is placed in a deposition chamber within the ALD device100. Once processing is complete, the wafer can be removed from thedeposition chamber via the same opening 120.

An ALD control system (not shown) is configured to control the ALDdevice 100 during processing of the wafer. For example, the ALD controlsystem can include a computer control system and electrically controlledvalves to control the flow of reactant and buffer gases into and out ofthe ALD device 100. The ALD control system can include modules such as asoftware or hardware component, such as a FPGA or ASIC, which performscertain tasks. A module may advantageously be configured to reside onthe addressable storage medium of the computer control system and beconfigured to execute on one or more processors.

FIG. 1B is a perspective view of the ALD device 100 showing the bottommember 112. The ALD device 100 further comprises a set of couplings102(a), 102(b), 104(a)-(d). In this exemplary configuration, ALD device100 includes four separate reactant vapor sources. Two of these reactantvapor sources are connected to the ALD device 100 via couplings 102(a),102(b). These gas sources can be pressurized or not. These vapor sourcescan be, for example, solid sublimation vessels, liquid bubblers or gasbombs. The third and fourth reactant vapor sources are connected to theALD device 100 via couplings 104(b), 104(c).

In one embodiment, each reactant vapor source has an associated inertgas source, which can be used to purge the reactant vapor lines afterpulsing the reactant. For example, the inert gas sources that areassociated with the reactant vapor sources connected to couplings 102(a)and 102(b) can be connected to couplings 104(a) and 104(d),respectively. The inert gas sources associated with the reactant vaporsources connected to couplings 104(b) and 104(c) can also connected tocouplings 104(b) and 104(c), respectively. These inert gas sources canbe pressurized or not. These inert gas sources can, be, for example,noble or nitrogen gas sources. The ALD control system (not shown)controls one or more valves to selectively allow or prevent the variousgases from reaching the ALD device 100.

The ALD device 100 can be configured to deposit a thin film on the waferwhen the wafer is inserted in the deposition chamber. In general, theALD device 100 can receive a first reactant gas via one of the couplings102(a), 102(b) or one of the couplings 104(b), 104(c). The ALD device100 can also receive inert gas via the couplings 104(a)-104(d). In oneembodiment, the inert gas enters the deposition chamber with the firstreactant gas to adsorb no more than a monolayer of the first reactant onthe wafer. By switching the appropriate valves (not shown), the flow ofthe first reactant gas is stopped preferably via an inert gas valving(IGV) arrangement and the deposition chamber and the gas lines are thenpurged with the inert gas from couplings 104(a), 104(b), 104(c), and104(d). After the deposition chamber and gas lines are purged, thedeposition cycle is continued with one or more of the other reactantgases. In one embodiment, the reactants from alternated pulses reactwith each other on the substrate or wafer surface to form no more than asingle monolayer of the desired product in each cycle. It should benoted that variations of true ALD operation can increase depositionspeed above one monolayer per cycle with some sacrifice to uniformity.

In embodiments of the ALD device 100, more than two reactant gases canbe sequentially flowed (separated by periods of purging) through the ALDdevice 100 in each cycle to form compound materials on the wafer. Excessof each reactant gas can be subsequently exhausted via gas exit 106(FIG. 1B) after adsorbing or reacting in the deposition chamber. The gasexit 106 may be connected to a vacuum pump to assist in the removal ofthe gases from the deposition chamber and provide a low pressurecondition in the deposition chamber. Furthermore, the entire ALD device100 can be pumped down to a low pressure by connecting any of the othercouplings on the bottom member 112 to a vacuum pump.

FIG. 2 is a cut-away section view of the ALD device 100 from FIG. 1Ataken along line 2-2. Within the ALD device 100 is a gas distributionsystem 202 (shown in more detail in FIG. 4) and a deposition chamber200, which is formed by a top or cover plate 314, bottom or base plate206, susceptor or wafer support 204 and exhaust launder 316. Located onupper and lower sides of the gas distribution system 202 and thedeposition chamber 200 are one or more reflector plates 208, 210. TheALD device 100 further includes a wafer support 204, a wafer supportheater 216, and a thermal switch 218.

The wafer support 204 is located within the ALD device and is configuredto support a substrate or wafer during the deposition process. The wafersupport 204 can be adapted to rotate within the deposition chamber 200.The wafer support heater 216 can be configured to heat the wafer support204. The thermal switch 218 can be provided on the top member 110. Thethermal switch 218 can be configured to monitor the temperature of thetop member 110. It will be understood that the system 100 includes othertemperature sensor and control mechanisms to maintain various surfacesof the system at desired temperatures.

The illustrated embodiment includes upper reflector plates 208 thatprovide a thermal barrier between the upper portion of the gasdistribution system 202 and the top member 110. Similarly, lowerreflector plates 210 provide a thermal barrier between the lower portionof the deposition chamber 200 and the bottom member 112. The reflectorplates 208 and 210 are also used to assist in radiatively heating thedeposition chamber within a low pressure environment. As illustrated inFIG. 2, the upper heater 114 is coupled to coils 212 which extendthrough the upper reflector plates 208. The coils 212 are configured toprovide heat through radiation to the upper portion of the gasdistribution system 202. Similarly, the lower heater 116 is coupled tocoils 214 which extend through the lower reflector plates 210 and heatthe lower portion of the deposition chamber 200. Alternatively, otherheating systems can be employed.

The gas distribution system 202 is configured to route reactant gasesentering via the couplings 102(a), 102(b), 104(b), 104(c) and inertgases entering via couplings 104(a)-(d) through the ALD device 100 (seeFIG. 1B). The gas distribution system 202 is further configured toselectively mix one or more of the inert gases entering via couplings104(a)-(d) with one of reactant gases entering via couplings 102(a),102(b), 104(b), 104(c) during a given pulse. The resulting mixtureenters the deposition chamber 200. After each pulse, the gasdistribution system 202 exhausts any unreacted reactant and inert gasesfrom the deposition chamber via gas exit 106, such as through purging.The term coupling is used to describe a gas flow connection between oneor more gas lines. The locations of the couplings shown herein are forillustrative purposes only and can be located at different locationsalong a gas line. Moreover, a gas line associated with a given couplingcan be configured to flow gas into or out of the gas distribution system202. As will be described below, the various couplings in the exemplaryembodiments described herein are designated to flow gases into or out ofthe gas distribution system 202. However, the invention is not limitedto the exemplary embodiments disclosed herein.

The order that the reactant gases are cycled through the ALD device 100depends on the desired product. To minimize any interaction between oneor more reactant gases prior to each gas entering the deposition chamber200, the inert gas entering via couplings 104(a)-(d) is periodicallycycled or continuously flowed through the ALD device 100 between pulsesof the reactant gases. In this way, the inert gases purge the depositionchamber 200. As will be explained below, various reactant gases andinert gases are systematically cycled through the ALD device 100 so asto form a deposit on the wafer inserted through the opening 120.

FIG. 3 is a perspective view of the deposition chamber 200 and the gasdistribution system 202 from the ALD device 100 of FIG. 1A. The gasdistribution system 202 comprises a plurality of gas lines, a mixerassembly 304, a transfer tube 310, and an intake plenum or manifold 312.The deposition chamber 200 includes a cover plate 314, a base plate 206,and an exhaust launder 316. The gas distribution system 202 is connectedto the deposition chamber 200 at the intake plenum 312

As best seen in FIG. 4, in this example, the plurality of gas linesinclude four reactant lines 300, 303, 309, 315 and eight buffer lines301, 302, 305, 307, 311, 313, 317, and 319. Each reactant line iscoupled with two of the buffer lines. Reactant line 300 is coupled tobuffer lines 301, 302. Reactant line 303 is coupled to buffer lines 305,307. Reactant line 307 is coupled to buffer lines 311, 313. Reactantline 315 is coupled to buffer lines 317, 319. The gas distributionsystem 202 can include greater or fewer reactant lines and buffer linesdepending on the configuration of the ALD device 100. Moreover, eachreactant line may or may not be coupled to two buffer lines. Forexample, one or more of the reactant lines may be coupled to the bufferlines while another reactant line is not. The reactant line that is notcoupled to buffer lines could be shut off by other means.

Each reactant gas line includes four couplings within the gasdistribution system 202. Reactant gas line 300 comprises couplings300(a), 300(b), 300(c), and 300(d). Reactant gas line 303 comprisescouplings 303(a), 303(b), 303(c), and 303(d). Reactant gas line 309comprises couplings 309(a), 309(b), 309(c), and 309(d). Reactant gasline 315 comprises couplings 315(a), 315(b), 315(c), and 315(d). Thecouplings for each reactant gas line are described below.

Coupling 300(a) couples the reactant gas line 300 with the coupling102(b) that leads to a reactant source (see FIG. 1B). Coupling 300(b)couples the reactant gas line 300 with the buffer line 302. Coupling300(c) couples the reactant gas line 300 with the buffer line 301.Coupling 300(d) couples the reactant gas line 300 with the mixerassembly 304.

Coupling 303(a) couples the reactant gas line 303 with the coupling104(b) that leads to another reactant source (see FIG. 1B). Coupling303(b) couples the reactant gas line 303 with the buffer line 307.Coupling 303(c) couples the reactant gas line 303 with the buffer line305. Coupling 303(d) couples the reactant gas line 303 with the mixerassembly 304.

Coupling 309(a) couples the reactant gas line 309 with the coupling104(c) that leads to another reactant source. (see FIG. 1B). Coupling309(b) couples the reactant gas line 309 with the buffer line 313.Coupling 309(c) couples the reactant gas line 309 with the buffer line311. Coupling 309(d) couples the reactant gas line 309 with the mixerassembly 304.

Coupling 315(a) couples the reactant gas line 315 with the couplingsource 102(a) that leads to still another reactant source (see FIG. 1B).Coupling 315(b) couples the reactant gas line 315 with the buffer line319. Coupling 315(c) couples the reactant gas line 315 with the bufferline 317. Coupling 315(d) couples the reactant gas line 315 with themixer assembly 304.

Buffer lines 301, 302, 305, 307, 311, 313, 317, and 319 comprisecouplings 301(a), 302(a), 305(a), 307(a), 311(a), 313(a), 317(a), and319(a), respectively.

In the embodiment illustrated in FIGS. 3 and 4, each coupling 301(a),305(a), 311(a), and 317(a) provides a flow path into the gasdistribution system 202. The coupling 301(a) couples the buffer line 301with the coupling 104(a) (see FIG. 1B). The coupling 305(a) couples thebuffer line 305 with the coupling 104(b) (see FIG. 1B). The coupling311(a) couples the buffer line 311 with the coupling 104(c) (see FIG.1B). The coupling 317(a) couples the buffer line 317 with the coupling104(d) (see FIG. 1B).

Each coupling 302(a), 307(a), 313(a), and 319(a) provides a flow pathbetween the gas distribution system 202 and the exhaust launder 316 viaconnectors 320(a)-(d). Connector 320(a) connects coupling 302(a) withthe exhaust launder 316. Connector 320(b) connects coupling 307(a) withthe exhaust launder 316. Connector 320(c) connects coupling 313(a) withthe exhaust launder 316. Connector 320(d) connects coupling 319(a) withthe exhaust launder 316. These connections contribute to the operationof inert gas valving (IGV).

In the embodiment shown in FIG. 3, the reactant gas lines 300, 303, 309,and 315 route reactant gases to the mixer assembly 304. The buffer lines301, 305, 311, and 317 route inert gases to the mixer assembly 304. Theresulting mixture (one reactant at a time with an inert gas) flowsthrough a transfer tube 310 to an intake plenum 312. The intake plenum312 distributes the mixture in a transverse direction with respect tothe flow path through the transfer tube 310. The mixture exits theintake plenum 312 into the deposition chamber 200 through the coverplate 314. As shown in FIGS. 2 and 3, the cover plate 314 lies adjacentto the base plate 206 and the two plates form a flow path there betweenfor the mixture to flow over the substrate or wafer placed on the wafersupport 204. The base plate 206 and the cover plate 314 havesubstantially rectangular outer perimeters.

While traversing the deposition chamber 200, the mixture pulse saturatesthe surface of the substrate. Adsorption or reaction occurs between thecurrent mixture and the surface of the substrate as left by the previouspulse may occur. After passing through the deposition chamber 200, themixture flows towards the exhaust launder 316. The exhaust launder 316is configured to collect excess of the mixture and any byproduct afterthe mixture has saturated the wafer. In an embodiment, a region withinthe exhaust launder 316 is at a lower pressure than the pressure in thedeposition chamber 200. A negative pressure source or vacuum can be inflow communication with the exhaust launder 316 and/or gas exit 106 todraw the mixture from the deposition chamber 200. The exhaust launder316 is in flow communication with the gas exit 106. The collectedmixture exits the deposition chamber 200 via the gas exit 106.

Still referring to FIG. 3, the mixer assembly 304 includes an upstreammember 306 and a downstream member 308. The upstream member 306 is inflow communication with the reactant gas lines and the buffer lines. Theupstream member 306 is configured to mix the reactant gas with the inertgas prior to the mixture entering the downstream member 308. Thedownstream member 308 funnels the mixture between the upstream member306 and the transfer tube 310. the downstream member 308 is generallyconfigured to minimize the tendency of the mixture to re-circulatewithin the downstream member 308 by continually reducing cross-sectionalarea of the flow path for the mixture.

FIG. 4 is a top plan view of the reactant gas lines coupled to thebuffer lines and the upstream member 306 of the mixer assembly. Betweencouplings 300(c) and 300(b), a buffer region 400(a) is formed in thereactant gas line 300. Between couplings 303(c) and 303(b), a bufferregion 400(b) is formed in the reactant gas line 303. Between couplings309(c) and 309(b), a buffer region 400(c) is formed in the reactant gasline 309. Between couplings 315(c) and 315(b), a buffer region 400(d) isformed in the reactant gas line 315. The buffer lines 301, 305, 311, and317, which form flow paths into the gas distribution system 202, coupleto their associated gas lines downstream of couplings 300(b) 303(b),309(b), and 315(b). In this way, gas entering via couplings 301(a),305(a), 311(a), and 317(a) enters the reactant lines 300, 303, 309, 315downstream of the reactant lines couplings with the buffer lines 302,307, 311, and 319. Fixed orifices can be placed at couplings 302(a),307(a), 313(a) and 319(a).

As seen in FIG. 3, couplings 302(a), 307(a), 313(a) and 319(a) are incommunication with the exhaust launder 316. The orifices create a higherresistance path for the gases to flow to the exhaust launder 316 andbypass the deposition chamber 200. In this way, during the pulse of areactant gas, a small portion of the reactant gas entering via couplings300(a), 303(a), 309(a) or 315(a) bypasses the deposition chamber andflows directly to the exhaust launder 316. The restriction created bythe orifice limits the amount of shunted reactant. During the purgestep, at least a portion of the inert gas entering via couplings 301(a),305(a), 311(a), and 317(a) creates a reverse flow towards couplings300(b) 303(b), 309(b), and 315(b) to form the buffer regions 400(a)-(d)within the reactant gas line. The buffer regions keep the reactant gasesfrom diffusing into the reactor during the purge steps or duringreactant flow of a reactant from one of the other reactant lines intothe mixer assembly 304.

For example, during an ALD processing step, reactant gas flows throughreactant line 300 towards the upstream member 306 of the mixer assembly.A small amount of this reactant gas is diverted to the buffer line 302and out through coupling 302(a) into the exhaust launder 316. The amountof gas that is diverted to the buffer line is dependent of the size ofthe fixed orifice at coupling 302(a). The size of the fixed orifice canbe changed to divert more or less of the gas into the exhaust launder316. The remaining reactant gas flows through the buffer region 400(a)to the coupling 300(c).

Inert gas may or may not be introduced through coupling 301(a) to pushthe reactant gas into the upstream member 306. If inert gas isintroduced through coupling 301(a), the inert gas joins the reactant gasat coupling 300(c) and flows to the upstream member 306. After the pulsestep, the reactant gas is purged from the gas line. Purging of the gasline can be accomplished by, for example, shutting off the flow of thereactant gas from coupling 300(a) and/or using the inert gas to impedethe diffusion of any remaining reactant gas into the upstream member306. The shutoff valve can be located outside of the heated area and canbe used to shut off the flow of the reactant gas. The inert gas can beintroduced through coupling 301(a) in an inert gas valving (IGV) processas described generally in U.S. patent publication number 2001/0054377,published on Dec. 27, 2001, the disclosure of which is herebyincorporated herein by reference.

A first portion of the stream of inert gas flow enters the buffer region400(a) and flows upstream or backwards towards the coupling 300(b). Asecond portion of the stream of gas flows downstream towards theupstream member 306. The first portion exits the reactant line 300 atthe end of the buffer region 400(a) and enters the buffer line 302.While the first portion is flowing through the buffer region 400(a), theremaining reactant gas between the shutoff valve upstream of coupling300(a) and coupling 300(b) is blocked from flowing or diffusing to theupstream member 306 without subjecting physical valves (which areremote) to the wear caused by high temperatures. The first portion formsa buffer or diffusion barrier (or inert gas valve) that impedes the flowof the reactant gas through the reactant line 300 to the mixer assembly304. By cycling the shutoff valve upstream of coupling 300(a), the ALDcontrol system is able to control between flowing and not flowing theinert gas in the buffer line 301. In this way, the ALD control system isable to quickly control whether the reactant gas entering the reactantline 300 via coupling 300(a) reaches the upstream member 306.Furthermore, during the purge step and subsequent pulses of otherreactant gases, the reactant gas in a “dead space” which is locatedbetween the shutoff valve upstream of the coupling 300(a) and coupling300(b) can be kept from diffusing into the upstream member 306. This maybe advantageous for ALD since the different reactant gases are keptseparated and only react on the surface of the substrate and not in thegas phase.

Whether the reactant gas entering the gas distribution system 202 viathe coupling 303(a) reaches the upstream member 306 is similarlycontrolled by flowing a gas through the buffer line 305 and into thereactant line 303 at coupling 303(c) and using a shutoff valve upstreamof coupling 303(a). A first portion of the gas entering the reactantline at coupling 303(c) forms the buffer 400(b). In this way, the firstportion of the gas impedes the reactant gas entering via the reactantline 303 from entering the upstream member 306. A second portion of thegas entering the reactant line at coupling 303(c) flows away from thebuffer region 400(b) and towards the upstream member 306.

Whether the reactant gas entering the gas distribution system 202 viathe coupling 309(a) reaches the upstream member 306 is similarlycontrolled by flowing a gas through the buffer line 311 and into thereactant line 309 at coupling 309(c) and using a shutoff valve upstreamof coupling 309(a). A first portion of the gas entering the reactantline at coupling 309(c) forms the buffer 400(c). In this way, the firstportion of the gas impedes the reactant gas entering via the reactantline 309 from entering the upstream member 306. A second portion of thegas entering the reactant line at coupling 309(c) flows away from thebuffer region 400(c) and towards the upstream member 306.

Whether the reactant gas entering the gas distribution system 202 viathe coupling 315(a) reaches the upstream member 306 is similarlycontrolled by flowing a gas through the buffer line 317 and into thereactant line 315 at coupling 315(c) and a shutoff valve upstream ofcoupling 315(a). A first portion of the gas entering the reactant lineat coupling 315(c) forms the buffer 400(d). In this way, the firstportion of the gas impedes the reactant gas entering via the reactantline 315 from entering the upstream member 306. A second portion of thegas entering the reactant line at coupling 315(c) flows away from thebuffer region 400(d) and towards the upstream member 306.

As mentioned above, the first portions of the gases which enter the gasdistribution system 202 via buffer lines 301, 305, 311, and 317 and formthe buffer regions 400(a)-(d), exit via buffer lines 302, 307, 313, and319. The gas exiting via buffer lines 302, 307, 313, and 319 enter theexhaust launder 316 without passing through the deposition chamber 200.In this way, the first portions of the inert gases bypass the depositionchamber 200 and are collected by the exhaust launder 316 downstream ofthe deposition chamber 200.

As mentioned above, the second portions of each gas which enter the gasdistribution system 202 via buffer lines 301, 305, 311, and 317 flowaway from the buffer regions 400(a)-(d) and enter the mixer assembly304. During reactant pulses, the second portions mix with one or morereactant gases from other reactant lines, which reach the mixer assembly304. Thus, the second portions flow through the deposition chamber 200.Depending on the current ALD processing step, gases may periodicallyflow through their respective buffer lines 301, 305, 311, and 317.

A reactant gas which the ALD control system desires to reach thedeposition chamber 200 flows through its respective reactant line andinto the mixer assembly 304. The ALD control system forms buffer regions400 in the reactant lines associated with the reactant gases which theALD control system does not want to reach the deposition chamber 200.The reactant gas which flows through the reactant line which does nothave a buffer region 400 mixes with the second portions of the one ormore inert gases which are simultaneously flowing through the otherreactant lines and into the mixer assembly 304. As explained above, thefirst portions of these gases form buffer regions in the other reactantlines and bypass the deposition chamber 200.

In one embodiment of the ALD device 100 which comprises four reactantgas lines, each reactant gas alternates in reaching the mixer assembly304. In this embodiment the reactant gas selected by ALD control systemflows into the mixer assembly 304 while inert or “buffer” gas flows inthe remaining three reactant lines. Continuing with this embodiment, thesecond portions of the gases flowing away from the buffer regions enterthe mixer assembly 304. The reactant gas of the pulse of interest thenmixes with the inert gas of the second portions in the mixer assembly304.

Further aspects and feature of the illustrated embodiment of the ALDdevice 100 can be found in U.S. patent application Ser. No. 10/841585,filed May 7, 2004, the entirety of which is hereby incorporated byreference herein.

FIG. 5 is a cross-sectional view of an embodiment of the transfer tube310, the plenum 312, the top plate 314 and the bottom plate 206described above. In particular, this figure shows the gas path from themixer assembly 304 to the deposition chamber 200. As shown in FIG. 5, ashim 500 can be positioned between the plenum 312 and the top plate 314.The shim 500 can be provided with a series of small injection holes 501,which are provided to create sufficient back pressure in the plenum 312to provide uniform flow across the deposition chamber 200. However, asshown in FIG. 5, this design can result in numerous recirculation cells502 between the deposition chamber 200 and transfer tube 310. Withinthese recirculation cells 502, reactants from the subsequent pulses maycollect. This may lead to CVD deposition within the deposition chamber200. Such CVD deposition is generally undesirable and can lead toparticle buildup within the deposition chamber 200. In addition, theshim 500 can produce a sharp contraction and then expansion of the gasflow. This can cause a sharp decrease in the temperature of the gasleading to condensation of the precursors in the gas stream.

FIGS. 6-9A illustrate an embodiment of a transfer member 510 and top(cover) plate 514. This embodiment seeks to reduce or eliminate therecirculation cells in the gas path by smoothing out the expansion andcontraction of the gas flow. FIGS. 6 and 7 are top perspective and planviews of the transfer member 510 and the top plate 514, respectively.FIG. 8 is a top plan view of the top plate 514 with the transfer member510 removed. FIG. 9 is a cross-sectional view taken through line 9-9 ofFIG. 7 and FIG. 9A is an enlarged view of a portion of FIG. 9.

As shown, the transfer member 510 forms a generally triangular shapedflow path that provides for gradual expansion of the gas from the mixer304. As best seen in FIGS. 8-9, the transfer member 510 in theillustrated embodiment includes a first portion 518 that is generallyadjacent to the mixer 304 and a second portion 520 that is generallyadjacent an opening 522 in the top plate 514. As shown in FIGS. 7 and 8,the first portion 518 includes a pair of horizontally divergent walls519 that expand in the horizontal direction at an angle A while thesecond portion 520 includes a pair of horizontally divergent walls 521that expand in the horizontal direction at an angle B. In oneembodiment, angle B is larger than angle A. In one embodiment, A isbetween about 5 to 45 degrees and B is between about 30 to 75 degrees.In the illustrated embodiment, the horizontally divergent walls aresubstantially straight. However, in a modified embodiment, thehorizontally divergent walls can be curved, arced, continuously varyingand/or segmented. In such an embodiment, the divergent walls can haveaverage or mean divergent angle in the ranges described above.

As shown in FIG. 9, the transfer member 510 includes a top wall 523which defines, in part, the height of a gas passage 511 defined by thewalls 519, 521, the top wall 523 and a top surface 525 of the top plate514. In one embodiment, in the first portion 518, the height h1 of a gaspassage 511 is preferably substantially constant. In the second portion520, the height h2 of the gas passage 511 gradually decreases in thedirection of the gas flow. In this manner, the volume of the secondportion 520 adjacent the opening 522 can be reduced as compared to theplenum 312 of FIG. 5. In addition, as the transfer member 510 expands inthe horizontal direction, the height of the gas path is reduced tosmooth out the expansion of the gas flow and increase back pressurewhich aid in spreading the gas flow across the chamber width. In theillustrated embodiment, the gas path defined by the passage 211 isgenerally parallel and opposite to the gas path in the depositionchamber 200 (see e.g., FIG. 11).

Another advantage of the illustrated embodiment is that the gas passage511 is formed between the transfer member 510 and a top surface 525 ofthe top plate 514. This “clamshell” arrangement makes it easier to cleanand refurbish the transfer member 511 as compared, for example, to atube. Specifically, when removed from the top plate 514, a large openingis created, which exposes the inner surfaces of the transfer member 511facilitating cleaning and refurbishing.

With reference now to FIGS. 8, 9 and 9A, the top plate 514 is providedwith the opening 522 to receive gas from transfer member 510. In oneembodiment, the opening 522 has a cross-sectional area that issubstantially equal to the cross-sectional area (with respect to gasflow) of the end of the second portion 520. In this manner, a smooth gasflow from the transfer member 510 into the top plate 514 is promoted.The opening 522 can have a generally elongated rectangular shape. SeeFIG. 8.

As shown in FIG. 9A, from the opening 522, the top plate 514 includes agradual contraction portion 524 that is connected to a narrowed region526. The contraction portion 524 includes a tapered or sloped wall 525,which gradually reduces the cross-sectional area of the gas flow. In theillustrate embodiment, the narrowed region 526 comprises a generallyrectangular slit of substantially constant cross-sectional area thatextends in a generally vertical direction down through the top plate514. The narrowed region 526 is the portion of the gas flow between themixer 304 and the deposition chamber 200 with the smallestcross-sectional area (with respect to gas flow). The narrowed region 526is configured to create sufficient back pressure to provide uniformflow, particularly along the width w (see FIG. 8) of the depositionchamber 200. The end of the narrowed 526 is in communication with anexpansion portion 528. The expansion portion 528 includes a slowed ortapered wall 529 that is configured to increase the cross-sectional areaof the gas flow such that the gas gradually expands as it enters thedeposition chamber 200. The outlet 530 of the expansion portion 528 isin communication with deposition chamber 200.

Advantageously, the narrowed region 526 is vertically and horizontallyelongated (a three-dimensional path) across the deposition chamber 200(see FIG. 8) as compared to individual holes (a substantiallytwo-dimension path) in the shim 500 described with reference to FIG. 5.For example, as compared to the individual holes, recirculation cellsand dead spaces in the x-plane (i.e. between holes) and in thez-direction (i.e., beneath the holes) are eliminated or reduced.Advantageously, this arrangement of the transfer member 510, plenum 512and top plate 514 also takes the gas from the mixer 304 and extends itover a portion of the deposition chamber 200. The gas flow is thenturned 180 degrees as it flows into deposition chamber 200.

Within the deposition chamber 200, dead volumes and/or recirculationcells can also be formed. For example, FIG. 10 is a schematicillustration of the substrate S and susceptor plate 204 of thedeposition chamber 200 of FIG. 1-4. As shown, there exists a gap g2between the substrate S and the susceptor plate 204 and a gap g1 betweenthe susceptor plate 204 and the base plate 206. In certaincircumstances, these gaps g1, g2 can be difficult to purge and mayharbor recirculation cells and/or be dead volumes.

FIG. 11 is a partial cross-sectional view of a modified embodiment ofthe bottom plate 600 and susceptor 602 of the deposition chamber 200taken along a line similar to line 9-9 of FIG. 7. FIG. 12 is a partialperspective view of the bottom plate 600 and susceptor 602. As shown, inthis embodiment, the base plate 600 has a sealing portion 604 with athickness t. The lower surface 605 of the sealing portion 604 sealsagainst the susceptor 602 to seal the reaction chamber. In oneembodiment, the end 606 of the sealing portion 604 has a thickness tthat is approximately equal to the thickness of the substrate positionedon the susceptor 602. Depending on the thickness of the substrate, thesealing portion 604 can have a thickness in the range from about 0.5 toabout 3 millimeters. In this manner, as the gas flows over the bottomplate 600 towards the substrate, the gas is only exposed to a shallowstep, which has a depth approximately equal to the thickness of thesubstrate. This reduces the size of or eliminates recirculation zonesand facilitates purging the deposition chamber 200.

Another advantage of the bottom plate 600 and susceptor 602 arrangementillustrated in FIGS. 11 and 12 is that the seal or contact surfacebetween the bottom plate 600 and the susceptor 602 is elevated ascompared the arrangement of FIG. 10. For example, in the illustratedembodiment, the lower surface 605 of the sealing portion 604 and thesubstrate are positioned substantially at the same vertical elevation.In one embodiment, the difference in elevation between the lower surface605 and the substrate is between about 0 to about 2 millimeters. Thisarrangement advantageously reduces the volume of the dead space betweenthe substrate and the bottom plate 604 and prevents or reduces theformation of recirculation cells in the deposition chamber 200.

FIGS. 13 and 14 illustrates in more detail the susceptor 602. FIG. 13 isa top perspective view of the susceptor 602, which has been rotated 180degrees with respect to the orientation shown in FIGS. 11 and 12. FIG.14 is a cross-sectional view of the susceptor 602 with a substratepositioned thereon.

In this embodiment, the susceptor 602 is configured such that thesubstrate S can be positioned off-center with respect deposition chamber200. In this manner, the gap g3 between the substrate and the interfacebetween the susceptor 602 and the bottom plate 600 can be displacedfurther away from the leading edge (with respect to gas flow) of thesubstrate S. In general, the leading edge of the substrate is positionednear the inlet into the deposition chamber 200 as compared to a trailingedge of the substrate, which is positioned near on outlet (exhaust) ofthe deposition chamber 200.

In another embodiment, the substrate can be centered (or substantiallycentered) on the susceptor. In such an embodiment, the susceptor can beoversized to increase the distance between the interface betweensusceptor 602 and the bottom plate 600 and the edge of the substrate. Inone embodiment, the susceptor 602 has a diameter that is at least about10% greater than the diameter of the substrate. In another embodiment,this diameter of the susceptor is at least about 25% greater than thediameter of the substrate. In another embodiment, the diameter of thesusceptor is between about 10% and about 25% greater than the diameterof the substrate. Such embodiments also provide for more space betweenthe leading edge of the substrate and the interface between thesusceptor and sealing surface. The oversized susceptor described abovecan also be used alone or in combination with the offset featuresdescribed in this paragraph to provide even more space the leading edgeof the substrate and the interface between the susceptor and sealingsurface.

Advantageously, for a susceptor of equivalent width and/or size, the gapg3 between the leading edge of the substrate and the interface betweenthe susceptor 602 and the bottom plate 600 can be increased. In thismanner, any recirculation cells caused by discontinuities between thesusceptor 602 and the bottom plate 600 are displaced further from theleading edge of the substrate S. Thus, in one embodiment, the center ofthe substrate positioned on the susceptor 602 is positionedasymmetrically and/or off-center with respect to the interface or sealbetween the susceptor 602 and the bottom plate 600. In a modifiedembodiment, the susceptor can have a non-round or asymmetrical shape tofurther distance the leading edge of the substrate from discontinuitiesbetween the susceptor 602 and the bottom plate 600.

As shown in FIG. 11, the susceptor 602 can include a plurality of pins609 that extend from the top surface of the susceptor 602 to constrainor confine movement of the substrate on the susceptor. The pins 609 canreplace shoulders or ridges (see e.g., the shoulder that creates the gapg2 in FIG. 10) that are sometimes used to constrain or confine movementof the substrate. Such shoulders or ridges can disadvantageously createrecirculation and/or dead zones. Thus, in one embodiment, a top area ofthe susceptor between the interface between the sealing surface and thesusceptor is substantially flat and does not include such shoulders orridges. Such an arrangement can eliminate or recirculation and/or deadzones.

With continued reference to FIG. 13 and with reference to FIG. 14, thesusceptor can include a recessed region 610, which is configured suchthat the substrate is only (or substantially only) contacted on itsedges (see FIG. 14). This embodiment helps to reduce wafer curvatureand/or susceptor doming from becoming problematic. In particular, wafercurvature and/or doming can cause a gap to form between the edge of thesubstrate and the susceptor. Gases can become trapped in this gap makingpurging inefficient and causing backside deposition. By contacting thesubstrate along its edges as shown in FIG. 14, wafer curvature and/ordoming will not cause a gap to form between the edge of the substrate Sand the susceptor 602. This eliminates or reduces the tendency for gasesto become trapped between the substrate and the susceptor. In oneembodiment, the recess region 610 has a depth between about 0.2 to 0.5millimeters. In another embodiment, the substrate S and susceptor 602are configured such that a continuous or substantially continuous sealis formed along the edge of the substrate S.

With continued reference to FIG. 13, the recess 610 can have a generallycircular shape such that the seal between the susceptor 602 and thesubstrate is also generally circular. In addition, as shown, the centerc of the recess 610 can be positioned “off-center” with respect to theouter edge of the generally circular susceptor 602. In this manner, theleading (with respect to gas flow) edge of the substrate can bedistanced from the sealing portion 604 of the bottom plate 600 ascompared to the trailing edge as described above. This allows the waferto be placed a greater distance from the recirculation cells in front ofthe wafer. Since the gas is swept across the wafer in a cross flowreactor, re-circulation cells on the rear seal between the susceptor andbase plate do not affect deposition uniformity as much.

FIG. 15 illustrates partial cross-sectional view of embodiment of anedge contact lift pin 620 that could be used in combination with thesusceptor 602 described above. As shown, the pin 620 can include a pinhead 622 that includes a notch 624 or beveled edge for securing thesubstrate S. The pin head 622 is configured to contact the edge of thesubstrate and lies generally at the interface between the susceptor 602and the recess region 610. The pin head 622 can be coupled to a pinshaft 626, which extends through openings 628 in the susceptor.

The pin 620 can be configured such that when the susceptor 602 is raisedinto the deposition chamber 200, the pin head 622 becomes recessedwithin a recessed region 630 formed in the susceptor 602. As thesusceptor is lowered, the pin head 622 can be raised with respect to thesusceptor 602. For example, as described in co-pending U.S. patentapplication No. ___/___,___, filed on Jan. __, 2006 under AttorneyDocket No. ASMEX.532A (the entirety of which is incorporated byreference herein), in one embodiment, to the raise the pin 620 from a“lowered” position seated in the recess 630, the substrate is moveddownward by a lifting mechanism. This downward movement causes thebottom surface the support pin 620 to contact a connector (not shown)positioned below the susceptor 602. The contact of the pin 620 with theconnector compresses a spring (not shown) surrounding a lower portion ofthe shaft 626. As the spring is compressed while the susceptor 602 ismoved downward, the spring attains a restoring force that willfacilitate relative “lowering” of the pin 620 when the susceptor 620 islifted next time. Accordingly, the combination of the spring and theplatform or “floor” for downward pin movement provided by the connectorpermits the pin to remain relatively fixed while the susceptor 602 movesup and down, without requiring the pin to be fixed relative to thedeposition chamber 200.

Although this invention has been disclosed in the context of certainpreferred embodiments and examples, it will be understood by thoseskilled in the art that the present invention extends beyond thespecifically disclosed embodiments to other alternative embodimentsand/or uses of the invention and obvious modifications and equivalentsthereof. In addition, while a number of variations of the invention havebeen shown and described in detail, other modifications, which arewithin the scope of this invention, will be readily apparent to those ofskill in the art based upon this disclosure. It is also contemplatedthat various combinations or sub-combinations of the specific featuresand aspects of the embodiments may be made and still fall within thescope of the invention. Accordingly, it should be understood thatvarious features and aspects of the disclosed embodiments can be combinewith or substituted for one another in order to form varying modes ofthe disclosed invention. Thus, it is intended that the scope of thepresent invention herein disclosed should not be limited by theparticular disclosed embodiments described above, but should bedetermined only by a fair reading of the claims that follow.

1. A substrate support for processing semiconductor substrates, thesubstrate support comprising a top surface with a recess, the recessbeing configured such that the top surface of the substrate support onlycontacts a substrate along an edge portion of the substrate.
 2. Thesubstrate support of claim 1, wherein the recess is asymmetricallypositioned on the top surface of the substrate support such that a firstedge portion of the recess is a first distance from a first adjacentedge portion of the substrate support, and a second edge portion of therecess is opposite from the first edge portion of the recess and ispositioned a second distance from a second adjacent edge portion of thesubstrate support, wherein the first distance is greater than the seconddistance.
 3. The substrate support of claim 1, wherein the recess has adepth from about 0.2 to about 0.5 millimeters.
 4. The substrate supportof claim 1, wherein the recess has a generally circular shape.
 5. Thesubstrate support of claim 4, wherein a center of the generally circularrecess is positioned off-center with respect to an outer edge of thesubstrate support.
 6. The substrate support of claim 1, wherein the topsurface of the substrate support is configured to form a generallycircular seal with the substrate when the substrate is positioned on thesubstrate support.
 7. The substrate support of claim 6, wherein a centerof the generally circular seal is positioned off-center with respect toan outer edge of the support.
 8. The substrate support of claim 1,wherein a top area of the susceptor between an edge of the susceptor andthe recess is substantially flat.
 9. The substrate support of claim 8,wherein the top area includes at least one pin.
 10. An atomic layerdeposition (ALD) thin film deposition apparatus, comprising: adeposition chamber configured to deposit a thin film on a wafer mountedwithin a space defined therein, the deposition chamber comprising a gasinlet that is in communication with the space, the deposition chamberfurther comprising a sealing portion that includes a sealing surface;and a susceptor configured to support the wafer within the space, thesusceptor configured to move vertically with respect to the depositionchamber between a first position in which the susceptor seals againstthe sealing surface and a second, lower position in which the susceptorno longer seals against the sealing surface; wherein, in the firstposition, a vertical distance between the interface between the sealingsurface and the susceptor and the wafer positioned on the susceptor isless than about 2 millimeters.
 11. The ALD thin film depositionapparatus of claim 10, wherein the interface between the sealing surfaceand the susceptor and the wafer positioned on the susceptor are locatedsubstantially at the same vertical elevation.
 12. The ALD thin filmdeposition apparatus of claim 10, wherein a top area of the susceptorbetween the interface between the sealing surface and the susceptor issubstantially flat.
 13. The ALD thin film deposition apparatus of claim10, wherein an end of the sealing portion has a thickness between about0.5 to about 3 millimeters.
 14. The ALD thin film deposition apparatusof claim 10, wherein the deposition chamber comprises a top plate and abottom plate and wherein the bottom plate forms, at least in part, thesealing portion and the top plate forms, at least in part, the gasinlet.
 15. The ALD thin film deposition apparatus of claim 10, whereinthe susceptor is configured such that when the wafer is positioned onthe susceptor a leading edge of the wafer with respect to gas flow ispositioned further from the sealing portion as compared to a trailingedge of the wafer.
 16. The ALD thin film deposition apparatus of claim15, wherein a diameter of the susceptor is at least about 10% greaterthan a diameter of the wafer.
 17. The ALD thin film deposition apparatusof claim 10, wherein a diameter of the susceptor is between about 10%and about 25% greater than a diameter of the wafer.
 18. An atomic layerdeposition (ALD) thin film deposition apparatus, comprising: adeposition chamber configured to deposit a thin film on a wafer mountedwithin a space defined therein, the deposition chamber comprising a gasinlet that is in communication with the space, the deposition chamberfurther comprising a sealing portion that includes a sealing surface;and a susceptor configured to support the wafer within the space, thesusceptor configured to move vertically with respect to the depositionchamber between a first position in which the susceptor seals againstthe sealing surface and a second, lower position in which the susceptorno longer seals against the sealing surface; wherein the susceptor isconfigured such that when the wafer is positioned on the susceptor inthe first position, a leading edge of the wafer, with respect to gasflow, is positioned further from the sealing surface as compared to atrailing edge of the wafer.
 19. The ALD thin film deposition apparatusof claim 18, further comprising a recess formed in the top surface ofthe susceptor, the recess asymmetrically positioned on the top surfaceof the susceptor such that a first edge portion of the recess is a firstdistance from a first adjacent edge portion of the susceptor, and asecond edge portion of the recess is opposite from the first edgeportion of the recess and is positioned a second distance from a secondadjacent edge portion of the susceptor, the first distance is greaterthan the second distance and the first edge portion of the recess ispositioned adjacent the gas inlet and the second portion of the recessis positioned adjacent the gas outlet.
 20. The ALD thin film depositionapparatus of claim 18, wherein the recess has a depth from about 0.2 toabout 0.5 millimeters.